The search for Christmas bargains has intensified as holiday shoppers flock in record numbers to shopping comparison sites and a fast-growing collection of sites that leak information on post-Thanksgiving sales.

Web-monitoring firm Hitwise reports that Google and Yahoo Search are referring 25% more visitors to shopping comparison sites than they did a year ago. Fueling that growth are several factors, including aggressive search engine marketing techniques, increasing consumer familiarity with sites such as Shopping.com, Shopzilla, and PriceGrabber, and fierce competition for every holiday E-commerce dollar, according to Hitwise.

Growing numbers of shoppers also are finding their way to so-called “Black Friday” sites. Sites such as bfads.com, Blackfridayads.com, and Gottadeal.com have popped up in recent months to leak advance notice of un-promoted sales slated to occur on the Friday after Thanksgiving, dubbed “Black Friday” because of its ability to lift struggling retailers out of the red and into the black of profitability.

The increased traffic at Black Friday sites has been enormous the past week. Bfads.com saw its traffic spike 519% from the previous week, while Blackfridayads.com and Gottadeal.com were up 437% and 138%, respectively.

Still, there’s evidence that all this online comparison shopping and deal-searching may not translate to a blockbuster holiday season for online retailers. A study released last month by Consumer Reports WebWatch found that one-fourth of adult Internet users have stopped buying things online out of fear of identity theft. In its survey of 1,501 users, WebWatch also found that 30% say they’ve reduced their use of the Internet in general to combat identity theft.